The AR-15, the military-style rifle that a gunman used to kill 17 people at a South Florida high school Wednesday, is at once a ferociously powerful weapon, a symbol of freedom and individualism, and an object of despairing worry about the future of democracy.

It is, depending on which political and social camp you belong to, “America’s rifle,” a way to “Control Your Destiny” or a killing machine that has no legitimate place in civilian life.

Every time a young man shoots up a school or other public gathering spot, the nation falls into a vituperative debate about whether the shooter’s weapon and the culture surrounding it are a pernicious, uniquely American problem in need of swift remedy.

The rifle, used in mass shootings in Newtown, Conn.; Las Vegas; San Bernardino, Calif.; and other grievous chapters, has become a barometer of the country’s debates not only about gun rights, but about the role of the individual, the proper limits on government, and the impact of video games, movies and other forms of pop culture on young people.

The AR-15 has come to carry connotations of heroism (a Remington ad said it gives “you the confidence and firepower to get the job done”), political resistance (tighter regulations could let government “subjugate Americans” and make them “live under tyranny,” a National Rifle Association executive said), fun (“killin’ zombies before it was cool,” reads another ad) and mass murder (high-capacity magazines have been used in more than half of mass shootings over four decades, according to several studies).

AR-15 rifles and their cousins are among the nation’s most popular and profitable weapons. The AR-15 fires one bullet with each pull of the trigger — thus, semiautomatic — but it is easily modified to shoot continuously until the trigger is released. A promotion for a $500 conversion device assures customers that a “new drop-in trigger promises to turn your basic AR into a (nearly) full-auto rifle, with no need for the onerous National Firearms Act licensing process.”

Nikolas Cruz, who police say confessed to the murders Thursday, bought his AR-15 legally, according to Peter J. Forcelli, the special agent in charge of the Miami office of the Bureau of Alcohol, Tobacco, Firearms and Explosives.

The AR-15 — its initials come not from “assault rifle” but from its original manufacturer, ­Armalite — is a descendant of the machine guns Nazi infantrymen used against Soviet forces in World War II.

In the United States, the weapon traces its origins to a contract the Pentagon gave in 1957 to ­Armalite, which designed it from plastic and aircraft-grade aluminum, rather than the wood and heavier metal that traditional ­rifles used. (The most popular such weapon worldwide is the ­AR-15’s Russian relative, the ­AK-47, or Kalashnikov, which dates to 1947 and has also been widely used by terrorists and mass murderers.)

The AR-15, later renamed the M-16, was designed to give U.S. soldiers the confidence that their firearm would efficiently mow down the enemy. The M-16 was the United States’ signature weapon in the Vietnam War; its descendants, chiefly the M4 carbine, are standard equipment to this day.

On the civilian market, the AR-15 didn’t sell terribly well for years, in part because of its connection with the Vietnam conflict, which was no one’s idea of a model of American greatness. Many gun enthusiasts didn’t like the AR-15 because it was so light; some dismissed it as feeling like a toy.

But the AR-15 found new life in 2004 when President George W. Bush allowed the ban on assault weapons that had been enacted under President Bill Clinton in 1994 to die.

And in 2005, Bush signed into law a measure protecting arms makers and dealers from liability for crimes committed with their products. The NRA called it “the most significant piece of pro-gun legislation in twenty years.”

AR-15s flew off the shelves. Sales spiked again during the Obama administration, when the country suffered a flurry of mass shootings, which in turn led to calls by Democrats to reinstate the ban on assault weapons. Persistent campaigns by the NRA and many Republican supporters of gun rights spread the idea that President Barack Obama intended to ban and confiscate Americans’ firearms, leading to a massive surge in sales. Obama never launched any such initiative.

Like abortion, immigration and political correctness, assault weapons cleave the country into sharply divided camps, separated by their vocabulary and coarsely cynical about each other’s motives.

Even its name is controversial. Opponents call it an “assault rifle,” arguing that it is designed solely to kill people and has no legitimate recreational use. Its defenders, who prefer to say “semiautomatic rifle” or “military-style ­rifle,” counter that it’s no different from other rifles and is suitable for hunting, target shooting and self-defense. The NRA dubbed it “America’s rifle.”

Over the past few decades, the military-style rifle has become a symbol not only of the political divide between gun-control people and gun rights people, but also of the cultural gulf between those who believe it is essentially American to take up arms in the service of righteous vengeance and those who believe society should focus instead on less-violent approaches to resolving conflict.

In portions of the country where guns are still commonly owned, AR-15s have become family fare. They are so easy to use — simple to fire, light to hold — that some retailers recommend them for children. The model is, according to the NRA, the most commonly used rifle in marksmanship training and competition.

Its 30-round magazine allows for rapid firing — even before modifications. And unlike handgun purchases, which carry a minimum age of 21 and require a three-day waiting period before a transaction can be completed, anyone 18 and over with a clean record can walk out of a Florida gun shop with an AR-15 in a matter of minutes. (Cruz is 19.)

Even as much of the advertising for the rifle centers on sport use and self-defense, the AR-15 has spawned a sprawling industry that serves and generates assault-rifle hobbyists. Enthusiasts sometimes describe the AR-15 as “the man’s Barbie doll,” an almost infinitely malleable collectible that owners can accessorize with infrared scopes, grips, flashlights and other add-ons. On average, AR-15 owners hold at least three versions of the firearm and spend more than $400 per rifle to accessorize them, according to industry research.

The weapon’s popularity has been enhanced by the AR-15’s regular appearances in hugely popular first-person-shooter video games such as the Call of Duty series, and by its omnipresence in action movies.

Studies conducted on the connection between violent behavior and depictions of military-style rifles in movies, TV and video games have often come to contradictory conclusions. Many of those who commit horrific crimes with such weapons had previously immersed themselves in gun culture. But it’s also true that more than 4 in 5 high school boys play video games, the most popular of which put the player in control of an assault weapon, and nearly all of those boys leave their fantasies in the world of imagination.

A gun industry trade magazine, Shooting Sports Retailer, advised gun shop owners to be aware that many new buyers are coming to the rifles through their love of violent video games. “Many of the new shooters attracted to tactical guns for their first firearms purchase will think that they know guns because they’ve played a lot of first-person shooter video games,” the magazine said.

In the wake of tragedies such as the killings at Marjory Stoneman Douglas High School, the nation briefly considers anew whether to ban such weapons. A Pew poll last year found that 68 percent of Americans favor banning assault weapons, including 48 percent of gun owners. Legislative initiatives rise and almost inevitably fall; in many parts of the country, the ultimate result is often an expansion of the kinds of places where assault weapons are permitted — schools, churches, government buildings.

After the massacre at the Pulse nightclub in Orlando left 49 people dead in June 2016, making it the worst mass shooting at that time, gun-control activists urged Florida lawmakers to ban semiautomatic weapons such as the ­AR-15. But bills modeled after the limits passed in Connecticut after the Sandy Hook Elementary School shooting died without getting a hearing last year. Refiled this year, they appear headed for the same fate.

“I would be happy if we could just have an adult conversation about this,” said state Sen. Linda Stewart, an Orlando-area Democrat who often wears rainbow-colored ribbons to remember the victims of the nightclub shootings. “I’m not real hopeful, and I am running out of time.”

The gun bills that are getting attention in Florida this year would relax restrictions; one would require the state to issue a concealed-carry permit within 90 days even if a background check is incomplete. Floridians hold more than 1.8 million concealed-carry permits, more than in any other state.

The latest school shooting led some pro-gun politicians to speak out against the AR-15. “I have hunted all my life,” Sen. Bill Nelson (D-Fla.) said on the Senate floor Thursday. “But an AR-15 is not for hunting. It’s for killing.”

Nelson, up for reelection this year, is expected to face Gov. Rick Scott, a Republican who got an A+ ranking from the NRA. Scott said Thursday that he supports keeping guns out of the hands of the mentally ill. He said nothing about assault weapons.